| 摘要: |
| 介形类对其生活的水体环境极其敏感，其壳体的物质几乎全部来自水体，因此壳体的化学组成常常用来反演古气候环境，然而对于青海湖介形虫壳体不同组成的控制因素存在诸多争议和不确定性。本文以沉积物捕获器在青海湖于2010年7月至2011年10月期间获得的介形虫样品为研究对象，结合CTD同步监测的湖水环境参数，探讨了青海湖现生的两个种属介形虫（意外湖花介和胖真星介）丰度和氧、碳同位素（δ18O、δ13C）的季节和年际变化特征及各自控制因素。结果表明，意外湖花介壳体的丰度比胖真星介的高一个数量级，但青海湖两种介形虫出现和丰度变化均受湖水温度直接控制。意外湖花介和胖真星介壳体的δ18O和δ13C均存在明显的年际和季节性变化及种属差异，而同步沉淀的自生碳酸盐却有较为均一的δ18O组成；两个种属介形虫壳体δ18O的年际差异是夏季水温系统差异的直接表现，而δ18O的季节性变化并不受控于降水和蒸发（P/E）比率，而可能主要与由高温诱发的大量自生碳酸盐沉淀有关；青海湖介形虫壳体δ13C的变化并不是单一因素控制的结果，可能也与湖水温度、自生碳酸盐沉淀等因素有关。本研究提出的自生碳酸盐沉淀对介形虫壳体δ18O和δ13C的控制作用，对于我们认识青海湖介形虫的环境意义及沉积物中介形虫壳体化学组成的古环境信息提取具有重要的启示意义。 |
| 关键词: 青海湖 介形虫 丰度 氧碳同位素 季节和年际变化 控制因素 |
| DOI：10.7515/JEE201303005 |
| CSTR： |
| 分类号:P597.2；Q958.8 |
基金项目:国家重点基础研究发展计划(2013CB956402)； 国家自然科学基金(41225015，40873082)
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| Seasonal and interannual variations in abundance and oxygen carbon isotopic compositions of ostracod shells from Lake Qinghai and their controlling factors: A case study on the sediment trap |
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LI Yan1,2, JIN Zhang-dong1
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1.State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment,
Chinese Academy of Sciences, Xi′an 710075, China; 2.University of Chinese Academy of Sciences, Beijing 100049, China
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| Abstract: |
| Ostracoda are extremely sensitive to the aquatic environment and the substances of their shells are almost entirely from the water body where they live, thus chemical compositions of the shells have been used to reconstruct paleo-climate and environment. However, the current explanations about the controlling factors of different compositions of ostracod shells from Lake Qinghai are controversial and uncertainty. In this study, on the basis of the ostracod samples collected by a time-series sediment trap in Lake Qinghai from July 2010 to October 2011, seasonal and interannual variations in abundance and oxygen-carbon isotopic (δ18O, δ13C) compositions of two species of ostracod shells (Limnocythere inopinata and Eucypris mareotica) and their respective controlling factors were discussed, by correlating with the state-of-the-art sensing data of lake water by a CTD (Conductance, Temperature, Depth). The results show that the abundance of Limnocythere inopinata shells is an order of magnitude higher than that of Eucypris mareotica, but both ostracoda′ emergence and abundance variations are controlled directly by the lake water temperature. The δ18O and δ13C of both Limnocythere inopinata and Eucypris mareotica shells have distinctly interannual and seasonal variations, with species differences as well, whereas authigenic carbonates precipitated synchronously from water column have relatively uniform δ18O. Interannual differences of δ18O of two species of ostracod shells reflect directly the systematic differences of the summer water temperature between 2010 and 2011. Nevertheless, seasonal variations of δ18O of two species are not controlled by precipitation and evaporation (P/E) ratio, but by the precipitation of plenty of authigenic carbonates induced by high water temperature. The variations of δ13C of ostracod shells in Lake Qinghai are not controlled by any single factor, but might be related with lake temperature, authigenic carbonates precipitation and other factors. The control of authigenic carbonates precipitation on δ18O and δ13Cof Lake Qinghai ostracod shells proposed in this study would be an important implication for further understanding environmental significance of ostracoda and for withdrawing paleo-environmental information from chemical compositions of ostracod shells in past sediment in Lake Qinghai. |
| Key words: Lake Qinghai ostracoda abundance oxygen and carbon isotopes seasonal and interannual variations controlling factors |
